Lpb-1 help with ideas

[Evil Armada]

Bit of a noob so be kind

I want to make a 18 volt lpb with variable gain. Instead of just the volume pot at the end of the circit. I dont really know how to go about this. I know with the 18 Volts the bais will need to change. Any links/advice on how I would go about this would be appretiated. Here's the schematic i'm using

http://www.muzique.com/schem/lpb1.gif

I know it won't be much of a lpb with these changes but I have a bunch of 2n5088's I want to use

[PRR]

> lpb with variable gain

Vary the "360" resistor. Gain will change. Bias won't change much.

> with the 18 Volts the bais will need to change.

No, not much. Here's a simulation for supply voltage from zero to 30V.



Below 5V it's just stuck. From 8V to over 20V it is in a good zone. Leave the bias alone.

Making the "360" resistor MUCH larger will skew the bias. As a "puzzle", I could figure a way to stabilize that.

But I have to wonder: why do you (think you) want variable gain?

You "need" the Volume pot for most useful conditions: the raw output can reach 2V on 9V batt, 5V on 18V batt, which are MUCH more than most guitar amp inputs want/need to see.

> Bit of a noob so be kind

Kindly, I suggest that as a "noob" you work with existing known-good pre-perfected plans. Just building a pedal is hard-enough.... look at the noobs (and non-noobs!) posting "Help!" Designing (even re-designing) is another level of learning. Beginning musicians hack at pre-written pieces like ChopSticks, I Can't Get No.., and Anna Magdalena before trying their own compostions. In fact Bach, who "could" put four notes together new, transcribed a lot of compositions by other composers.

[Evil Armada]

I've built a couple of simple pedals... And a simple tube amp. So I just wanted to have a go at modding something. Thankyiu for the help. I may not even end up using the 18v. Maybe I'll do a 2 knob lpb. After reading the booster article on amz I just thought it would be cool to control the compression on the pedal. Controling the 360 resistor would do that right? Is there any articles explaining how to bias transisters? I've been doing a lot of study on tubes and I'm just getting into transisters designs

[Caferacernoc]

If you made the 360 resistor a 1 or 2k pot you would have some ability to control gain and the slight clipping a LPB can have with loud humbuckers. I usually build them with a 1k resistor fixed. It's loud enough and slightly cleaner.

[Mark Hammer]

The question that needs to be asked is "Why 18V?".

[Evil Armada]

Just an idea for more headroom. It's ok i'm just going to use 9v

[darron]

I have a circuit that is somewhere between an range master and a SHO. I also use adjustable gain instead of a volume pot at the end. I use a pnp germanium transistor though so clipping isn't as much of a problem. As said, replacing that 360 resistor is the trick. 0ohm gives max gain and for me around 5k gives unity, so you could just use a 5k/2k LIN pot.

To bias, instead of a couple of resistors to +/- which already add to around 500k, I just use a 500k trim pot with each end connected to +/- and the bias voltage coming from the wiper.

When I don't use near max gain though I can hear a bit of noise so it's mostly only good at 75%-100%.